Troubleshooting and Mitigation of Corrosion: Cathodic Protection Technique
Troubleshooting and Mitigation of Corrosion by Cathodic Protection Technique use to mitigate corrosion of underground or submerged metallic structures.
Cathodic protection is a technique used to control naturally occurred corrosion that can deteriorate metal surface by making it the cathode of an electrochemical cell. A procedure by which a structure (buried pipeline, ship hulls, oil drilling rig, etc.) is protected against corrosion.
Cathodic Protection systems are used all over the globe to protect the pipeline, high-temperature subsea pipeline, submarine pipeline, water treatment plants, above and underwater storage tanks, ships and boat hulls, offshore oil and gas production platforms, reinforcement bars in concrete structures by mitigating corrosion damage to active metal surfaces.
Corrosion occurs when two dissimilar metals are not in physical contact but electrically submerged in an electrolyte substance such as water, soil, or concrete. In this process metal conducting path between the two dissimilar metal allow a pathway through which free electrons move from the positive terminal (anode) to the negative terminal (Cathode).
A direct current is impressed onto the structure by means of a sacrificial anode or a rectifier.
The most common metal to be protected by CP is steel.
Working of Cathodic Protection:
Cathodic Protection is an electrochemical technique to prevent external or internal corrosion on a metallic surface which is connected or submerged in an electrolyte substance. Cathodic protection connects the base metal at risk (steel) to a sacrificial metal that corrodes in lieu of the base metal and this direct current can be delivered by sacrificial anodes.
Thus, there are two systems for supplying the necessary current:
- Sacrificial Anode System (Galvanic Protection)
- Impressed Current Cathodic Protection System (ICCP)
Sacrificial Anode System (Galvanic Protection):
Sacrificial anodes generally come in three metals:
Common sacrificial anodes are:
- Mg (Magnesium): Magnesium has the most electro potential of the three. It is more suitable for on-shore pipelines or buried pipelines where the electrolyte resistively in higher.
- Zn (Zinc) and Al (Aluminum) are generally used in seawater, where the resistivity is generally lower. It is suitable for submerged marine structure (oil platforms, ship hulls, offshore pipelines, in salt-water-cooled marine engines, and on boat propellers etc.)
- Electrical output is given by the current capacity (A. hr/ Kg)